ABO System

How is blood classified? Blood is classified according to the nature of the chemical substances known as antigens or markers, which are microscopic substances found on the surface of the red blood cells. They present on RBC as glycolipids and as glycoproteins expressed on the surface of the RBC.

Antigens in the Human blood group: Antigens in RBC Antigens in WBC Antigens in Platelet.

Antigens are controlled by chromosomes: Chromosome 9 ABO blood group Chromosome 1 Rhesus blood group Chromosome 19 Lewis blood group

20th Century Transfusions 1901 Karl Landsteiner Discovers A, B, O Blood Groups

Blood Groups Most of them are proteins (such as Rh, Duffy and Kidd), but some are carbohydrates attached proteins (glycoproteins such as ABO, P and Lewis). More than 254 different blood group antigens have been reported.

Although there are many blood group systems with several sub- types, the two best-known ways of classifying blood are the ABO group system and the Rhesus (Rh) type system.

The RBCs of each individual were found either to lack or to have one or both of the two antigens, A and B. In addition, the serum of each subject contained naturally occurring directly agglutinating antibodies that recognized the antigens absent from their own RBCs.The RBCs of each individual were found either to lack or to have one or both of the two antigens, A and B. In addition, the serum of each subject contained naturally occurring directly agglutinating antibodies that recognized the antigens absent from their own RBCs.

There are interesting variations in the frequencies of these blood types in different human populations. The ABO group is identified by a letter of the alphabet, so a person can mainly belong to the A, B, AB or O blood group.

ABO system Antigens: There are three Antigens belong to this system, A, B and H. Comments –Serum from group A individuals contains naturally occurring anti-B –Serum from group B individuals contains naturally occurring anti-A –Serum from group A B individuals contains no Abs. –Serum from group O individuals contains naturally occurring anti-A and Anti-B

Serologists have defined two common subgroups of the A antigen. Approximately 20% of group A and group AB individuals belong to group A2 and group A2B, respectively, the remainder belonging to group A1 and group A1B. These subgroups arise as a result of inheritance of either the A1 or A2 alleles.

A2 red cells have fewer A antigen sites than A1 cells. In addition, the number of A antigens on A1 RBCs is approximately five times more than on A2 RBCs. The plasma of group A2 and group A2B individuals may also contain anti-A1 The H antigen content of red cells depends on the ABO group and when assessed by agglutination reactions with anti-H, The strength of reaction tends to be graded O > A2 > A2B > B > A1 > A1B. Other subgroups of A are occasionally found (e.g., A3, Ax) that result from mutant forms.

Blood Group Antibodies: In vitro characteristics of the ABO Ab: Naturally Occurring Antibodies " ABO antibodies, in the absence of the corresponding antigens, appear during the first few months after birth, probably as a result of exposure to ABH antigen-like substances in the diet or the environment (i.e., they are “naturally occurring”) Immunoglobulin class IgM ''complete'' that directly agglutinate the appropriate antigen- positive RBCs.

- Optimal technique RT or below ''cold reacting''. - Neutralization Saliva from A secretors - Complement binding Yes '' very actively'' some hemolytic (rare in A2) - Do not cross the placenta

, Blood Group Antigens on RBCs Antibodies in SerumGenotypes A AAnti-BAA or AO BBAnti-A BB or BO ABA and BNeitherAB O Neither Anti-A and anti-BOO

Secretors and Nonsecretors People make A, B, and H secretor substances. The substances appear as Ags in the body fluids. The ability to secrete A, B, and H substances in water- soluble form is controlled by FUT2 (gene). Secretors have H substance in the saliva and other body fluids together with A substances, B substances, or both, depending on their blood group. Can be homozygous Se Se - Produce ABH substances Heterozygous Se se - Produce ABH substances Allelemorphic se se - No production of ABH substances. Only traces of these substances are present in the secretions of nonsecretors, although the antigens are expressed normally on their red cells and other tissues.

Inheritance of ABO ABO & RH genes are not linked Genotype: Sum of the genes. Phenotypes: product of the genes.

Allele from the mother Allele from the father Genotype of offspring Blood types of offspring A AAA A ABAB AO AOA BA AB BBBB B BO BOB O OOOO

Universal Donor and Recipient Universal Donor Group O –Carries no A or B antigens –Packed and processed units have little antibody Universal Recipient Group AB –Patient has no anti-A or anti-B present –Cannot lyse any transfused cells –Beware: other antibodies may be present

ABO mismatched transfusions: –Rare –May be life threatening –Can be caused by technical or clerical error –Intravascular haemolysis –More severe in group O patients